the ratio of the number of followers you have on Twitter to the number of people who follow you.Aren't those numbers the same?

Okay, facetious nit-picking aside, I think some people might use it just to get the quip it gives you based on your ratio. (e.g., "6.12: Popular Aren't I?") But yeah, you could just run calc.exe and do this. Or Google. Or anything else, really.

Yeah, but Calc doesn't give you a cool badge that you can use on your blog to show people how Twitter cool you are!

The site really started out as kind of a joke. But then people started actually using it. So I went with the flow. Now with the history and some other updates people are using it more and more. ... and talking about it more - Thanks!

The value isn't so much in the ability to divide two numbers, but in having a link which documents this statistic. When you have a shiny website which documents your popularity, you can link to it (or even twitter about it, which they actively encourage you to do) and show off how incredibly awesome you are, which has social value.